That is one unusually sized space for a grow. 8 plants will grow there fine, if you prepare the space properly.
A 400 HPS won't cover the space well to the 6' ends, and then there's the heat.
A couple of 250's would light the space up well, and then there's the heat.
CFL's on some kind of rig to cover the space would also work. And then there's the heat.
Personally, I'd worry how you're going to vent the room